Any boiler can become dangerous when there is only a single outlet and it
becomes plugged. My friend had a kitchen pressure cooker explode when the
pressure maintaining device plugged and the emergency relief valve was also
plugged.
Old railroad steame engines usually had 3 pressure relief valves all set
about 1 psi apart.
Bad thing about a boiler explosion is not only the boiler steam (and it can
be way over 212 degrees, depending on the pressure) but the water volume in
the boiler, which can also be way over 212 degrees. Again depending on the
pressure. When the boiler ruptures, all the remain liquid water immediately
flashes into steam, with the loss of the pressure. I believe the volume
ratio is something like 10,000 to 1 cubic units, of water when turning into
steam. And when this steam condenses, you have water at less than 211
degrees. Many ways to burned badly.



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